To what some are calling an epidemic of twins. The fertility health for couples that want children. It's also a boom in multiple births. And now, fertility doctors are trying to cut that. Reporter: The idea that two is better than one or that twins are always twice as nice, maybe notions of the past when it comes to fertility treatment. A growing number of couples are now attempting pregnancy with just a single embryo and having great success. Doctors are saying there's a new epidemic in fertility. A twin epidemic. Nearly half of all babies born with the help of advanced fertility are twins, according to new federal numbers. And twins, while twice the gift, can also increase the risks. 37% are born premature. Carrying twins are associated with a significantly increased rate of multiple pregnancy complications. The largest of which is premature birth. Reporter: Apparently it no longer pays to double-down in the high-stakes world of ibf treatment, at least according to the study by the medical associations of new jersey. When you can pick an embryo up front, you don't need to put back two. Reporter: The traditional theory had been use multiple embryos to increase the chance of pregnancy. Now, doctors are recommending a new approach. One embryo at a time. We can determine in advance which embryos have a good opportunity to implant. Reporter: Dr. Richard scott headed up the study that found women who had one embryo at a time transferred after chromosome screening, versus two embryos with no screening, resulted in roughly equivalent delivery rates. 14-month-old bennett is part of the 61% success rate. I was glad I didn't have to choose. Reporter: Bennett's mom, carla, participated in that study and was among the women who had only one embryo transferred. Twins scared me, especially after carrying one child. The idea of carrying two children is pretty frightening. Reporter: Dr. Scott contends the new technology that allows them to screen and select the viable embryo, makes the success rate almost as good as when two or more are used. They need fewer treatment cycles. Reporter: Many women who undergo ibf can only do it once. And wanted to double their odds. But this new technology could limit some of the rolling of the dice aspect. This is something that women will have to discuss on a case-by-case basis, with their doctor, based on their age and their particular fertility problem. Dr. Besser's mantra. Thank you, linsey. Coming up, very special performance from the cast of

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